Strontium Phosphate Composite Designed to Red-Emission at Different Temperatures

Eu(3+)-doped Sr(10)(PO(4))(6)(OH)(2)–Sr(3)(PO(4))(2) (SrHAp-TSP) composites were obtained via the microwave-stimulated hydrothermal method and post-heat-treated from 750 to 950 °C. Concentration of the Eu(3+) ions was set to be 0.5, 1, 2, 3, 5 mol% in a ratio of the strontium ions molar content. The structural and morphological properties were investigated by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FT-IR) techniques. The average particle size of the studied materials annealed at 750, 850 and 950 °C were counted about 100, 131 and 173 nm, respectively. The luminescence properties depending on the dopant ion concentration, heat-treatment temperature, excitation wavelength and temperature were investigated. In the emission spectra, a broad peak corresponding to the 4f(6)5d(1) → 4f(7) ((8)S(7/2)) emission of Eu(2+) ions as well as narrow 4f-4f transitions typical for Eu(3+) ions can be observed. The luminescence intensity of the 1 mol% Eu(3+):Sr(10)(PO(4))(6)(OH)(2)–Sr(3)(PO(4))(2) was measured depending on the ambient temperature in the range of 80–550 K. The CIE 1931 (International Commission on Illumination) chromaticity diagram was determined from emission spectra measured in 80, 300 and 550 K. The reduction mechanism of the Eu(3+) to the Eu(2+) was explained by the charge compensation mechanism based on the Kröger–Vink-notation. The decay times were measured and the Judd–Ofelt (J–O) theory was applied to analyze the observed structural and spectroscopic features.